Last week the Tories were increasingly resigned to defeat in the Eastleigh by-election but the Rennard allegations, combined with a poll (conducted before the story broke) putting them four points ahead of the Lib Dems, have given the party renewed hope of winning the seat. The odds on a Lib Dem victory have lengthened, while those on a Conservative victory have narrowed.

My sense, however, is that the Rennard story, like the Huhne scandal, will have little effect on the outcome. As one Lib Dem tells the Times today, "If Chris Huhne lying isn’t going to derail us then a peer that very few people have heard of is not going to harm us". Nick Clegg was almost certainly right when he suggested this morning that local issues such as planning would continue to dominate.

But this doesn't alter the fact that Eastleigh is now even more of a must-win seat for the Tories. The Huhne and Rennard scandals, notwithstanding their limited influence on voters, give the press every excuse they need to portray any defeat as a humiliating set-back for Cameron. In such circumstances, the only consolation for the Tories will be that Labour, which is set to finish in fourth place behind UKIP, will face some tough questions of its own.

No one ever expected Labour, which polled just nine per cent in Eastleigh at the general election, to win the seat. The swing required would put the party on course for a majority of 362. But as the only large opposition party, not least one which claims to be a "one nation" force, it should be performing much better midway through the parliament.